1. 概念

keepalived是什么
    keepalived是集群管理中保证集群高可用的一个服务软件，用来防止单点故障。

keepalived工作原理
    keepalived是以VRRP协议为实现基础的，VRRP全称Virtual Router Redundancy Protocol，即虚拟路由冗余协议。

虚拟路由冗余协议，可以认为是实现路由器高可用的协议，即将N台提供相同功能的路由器组成一个路由器组，这个组里面有一个master和多个backup，master上面有一个对外提供服务的vip（该路由器所在局域网内其他机器的默认路由为该vip），master会发组播，当backup收不到vrrp包时就认为master宕掉了，这时就需要根据VRRP的优先级来选举一个backup当master。这样的话就可以保证路由器的高可用了。

2、Nginx+keepalived实现七层的负载均衡

Nginx通过Upstream模块实现负载均衡

主机名	ip	系统	用途
Proxy-master	172.16.147.155	centos7.5	主负载
Proxy-slave	172.16.147.156	centos7.5	主备
Real-server1	172.16.147.153	Centos7.5	web1
Real-server2	172.16.147.154	centos7.5	Web2
Vip for proxy	172.16.147.100

一、实施过程 
1、选择两台nginx服务器作为代理服务器。
2、给两台代理服务器安装keepalived制作高可用生成VIP
3、配置nginx的负载均衡

# 两台配置完全一样
[root@proxy-master ~]# vim /etc/nginx/nginx.conf
user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log;
pid /run/nginx.pid;
include /usr/share/nginx/modules/*.conf;
events {worker_connections 1024;
}
http {log_format  main  '$remote_addr - $remote_user [$time_local] "$request" ''$status $body_bytes_sent "$http_referer" ''"$http_user_agent" "$http_x_forwarded_for"';access_log  /var/log/nginx/access.log  main;sendfile            on;tcp_nopush          on;tcp_nodelay         on;keepalive_timeout   65;types_hash_max_size 2048;include             /etc/nginx/mime.types;default_type        application/octet-stream;include /etc/nginx/conf.d/*.conf;upstream backend {server 172.16.147.154:80 weight=1 max_fails=3 fail_timeout=20s;server 172.16.147.153:80 weight=1 max_fails=3 fail_timeout=20s;}server {listen       80;server_name  localhost;location / {proxy_pass http://backend;proxy_set_header Host $host:$proxy_port;proxy_set_header X-Forwarded-For $remote_addr;}}
}

Keepalived实现调度器HA
1. 主/备调度器安装软件

[root@proxy-master ~]# yum install -y keepalived
[root@proxy-slave ~]# yum install -y keepalived
[root@proxy-master ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.bak
[root@proxy-master ~]# vim /etc/keepalived/keepalived.conf
! Configuration File for keepalivedglobal_defs {router_id directory1   #辅助改为directory2
}vrrp_instance VI_1 {state MASTER        #定义主还是备interface ens33     #VIP绑定接口virtual_router_id 80  #整个集群的调度器一致priority 100         #back改为50advert_int 1authentication {auth_type PASSauth_pass 1111}virtual_ipaddress {172.16.147.100/24   # vip}
}

备用机器也添加配置文件

[root@proxy-slave ~]# cp /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf.bak
[root@proxy-slave ~]# vim /etc/keepalived/keepalived.conf
! Configuration File for keepalivedglobal_defs {router_id directory2
}vrrp_instance VI_1 {state BACKUP    #设置为backupinterface ens33nopreempt        #设置到back上面，不抢占资源virtual_router_id 80priority 50   #辅助改为50advert_int 1authentication {auth_type PASSauth_pass 1111}virtual_ipaddress {172.16.147.100/24}
}

启动keepalived 主备都启动

[root@proxy-master ~]# systemctl enable keepalived
[root@proxy-slave ~]# systemctl start keepalived
[root@proxy-master ~]# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00inet 127.0.0.1/8 scope host lovalid_lft forever preferred_lft foreverinet 172.16.147.100/32 scope global lovalid_lft forever preferred_lft foreverinet6 ::1/128 scope host valid_lft forever preferred_lft forever
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000link/ether 00:0c:29:ec:8a:fe brd ff:ff:ff:ff:ff:ffinet 172.16.147.155/24 brd 172.16.147.255 scope global noprefixroute dynamic ens33valid_lft 1115sec preferred_lft 1115secinet 172.16.147.101/24 scope global secondary ens33valid_lft forever preferred_lft forever

现在就实现了两台机器的高可用，两台高可用的机器都作为另外两台nginx服务器的负载均衡器，一台机器down掉了，会自动漂移到另一台备用机器上继续访问